Collaborative Research: Biogeochemical drivers of interspecies electron transfer from iron reducers to methanogens

铁还原和甲烷生成是自然界中最常见的两种微生物反应。在铁还原过程中，微生物呼吸出三铁，即铁锈中的铁。在产甲烷过程中，微生物产生甲烷，甲烷是天然气的主要成分，也是一种强有力的温室气体。一些铁还原剂和产甲烷菌（驱动反应的微生物）可以通过种间电子转移（IET）共享能量资源来相互合作。然而，大多数预测模型假设，由于能源竞争，产甲烷菌和铁还原剂不会共存，并且只允许在铁质矿物耗尽的地方产生甲烷。如果不能同时考虑IET和竞争，可能会导致基于过程的甲烷产量估计出现误差。此外，IET的环境驱动因素尚未确定，限制了模型预测甲烷通量如何随环境变化而变化的能力。这项研究将创建一个新的甲烷生成模型，将竞争和合作的相互作用联系起来。该模型将提高预测甲烷生成和管理自然和工程系统（包括土壤、含水层、垃圾填埋场和废水处理系统）碳预算的能力。这项研究还将为本科生和研究生提供培训，并通过参加堪萨斯路易斯斯托克斯少数民族参与联盟的暑期研究项目和面向中学女生的暑期拓展活动，增加代表性不足的群体对科学的参与。本研究的研究目标是：1)确定推动产甲烷菌和铁还原剂在竞争和IET之间相互作用的环境驱动因素；2)确定产甲烷菌和铁还原剂之间相互作用的变化如何影响甲烷生成；3)评估酶性质和环境化学在确定相互作用性质中的耦合作用。为了实现这些目标，该研究将把生物反应器实验结果与动态酶建模相结合。生物反应器实验将研究相互作用和甲烷产量如何随关键的生物地球化学因素而变化，包括pH值、三铁来源、电子供体和亚铁的可用性。建模分析将考虑酶动力学和反应能量学来模拟亚细胞/酶水平的反应，实验结果为验证提供基础。在实验和模拟中，产甲烷菌和铁还原剂之间的竞争和共生都是可能的，这使得这项研究能够解决相互作用和甲烷生成是如何随着环境化学而进化的。此外，研究结果将通过定义这种相互作用的环境背景，为评估铁还原剂和产甲烷菌之间IET的环境意义创建路线图。这样做，研究结果将提供必要的工具，以促进我们对全球甲烷循环的生态基础的理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Iron reduction and methanogenesis are two of the most common microbial reactions in nature. During iron reduction, microorganisms respire ferric iron, the form of iron in rust. During methanogenesis, microorganisms make methane, the primary component of natural gas and a potent greenhouse gas. Some iron reducers and methanogens, the microbes that drive the reactions, can cooperate with one another by sharing energy resources through interspecies electron transfer (IET). However, most predictive models assume that methanogens and iron reducers do not coexist, due to competition for energy sources, and only allow methane generation where ferric minerals have been depleted. Failure to account for both IET and competition may introduce error in process-based estimates of methane production. Moreover, environmental drivers of IET have not been identified, limiting the ability of models to predict how methane fluxes vary with environmental change. This study will create a new model for methanogenesis that links competitive and cooperative interactions. The model will improve the ability to predict methane generation and manage carbon budgets in natural and engineered systems including soils, aquifers, landfills, and wastewater treatment systems. The study will also provide training to undergraduate and graduate students and increase involvement of underrepresented groups in science through participation in the Kansas Louis Stokes Alliance for Minority Participation summer research program and summer outreach events for middle-school girls.Research goals of this study are to: 1) identify environmental drivers that push interactions of methanogens and iron reducers between competition and IET, 2) determine how changes in interactions between methanogens and iron reducers affect methane generation, and 3) evaluate the coupled role of enzyme properties and environmental chemistry in determining the nature of interactions. To achieve these goals, the study will integrate the results of bioreactor experiments with dynamic enzyme modeling. The bioreactor experiments will examine how interactions and methane production vary with key biogeochemical factors, including pH, ferric iron source, and the availability of electron donors and ferrous iron. The modeling analysis will consider enzyme kinetics and reaction energetics to simulate reactions at a subcellular/enzymatic level, with experiment results providing a basis for validation. Both competition and syntrophy between methanogens and iron reducers will be possible in the experiments and simulations, allowing the study to resolve how interactions and methane generation evolve with environmental chemistry. Moreover, study findings will create a roadmap for evaluating the environmental significance of IET between iron reducers and methanogens by defining an environmental context for this interaction. In doing so, study results will provide the tools needed to advance our understanding of ecological underpinnings of the global methane cycle.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.